Steve Viksten, who helped develop the 1990s Nicktoon Hey Arnold! and was the show’s most prolific writer, has died. Hey Arnold!creator Craig Bartlett posted a memorial to Viksten on Facebook yesterday, June 24, stating “Steve Viksten, who wrote many of my favorite Hey Arnold! stories, died yesterday. I was lucky to be near to so much talent for so long. RIP.” Viksten was 54.

In addition to writing for Hey Arnold!, Viksten provided the voice for several of the show’s characters—most notably Oskar Kokoshka, the shiftless, con-artist-in-residence of Hey Arnold!’s central boarding house. True to the show’s understanding treatment of its characters, Oskar proved to be more than a selfish opportunist, a hidden warmth unearthed in Viksten’s sad-sack characterization. Oskar’s ambiguously Eastern European accent (“his impersonation of our former boss Gabor Csupo,” Bartlett told The A.V. Club, “probably the most imitated accent in our business”) likely echoes through the memories of viewers who grew up with Hey Arnold!, a sleepy voice intoning “Look everybody, I’m petting the kitty” and “You keep the money” in moments long since clipped and posted to YouTube.

With Hey Arnold! credits including “Arnold’s Hat” (in which the protagonist’s lost headwear leads to the first onscreen reminisces of his absent parents) and “Stoop Kid” (which deals with a Boo Radley type ending his self-imposed detainment on the front steps of his building), Viksten’s episodes were critical to forming the show’s internal history and sense of inner-city lore. In addition to working on Hey Arnold! (the movie adaptation of which he also wrote), Viksten scripted episodes of Rugrats, Recess, and Duckman. In 2011, he co-wrote the 12th episode of The Simpsons’ 22nd season, “Homer Scissorhands,” an effort that once more put his words in the mouths of Dan Castellaneta and Tress MacNeille, who voiced Arnold’s grandparents on Hey Arnold!